The next generation of armor must exhibit exceptional ballistic penetration resistance, reduced weight, and low production costs. Emerging armor composites must address threats from fragmentation and small arms fire. Subsequently, novel armor composites must find an optimal balance between penetration resistance performance and minimum areal densities.
Several recent approaches have incorporated both monolithic and composite layers of polymer or polymer/metal coatings on the front surfaces of high hard steel (HHS) armor plates. Different configurations, such as Dragonshield armor, have improved ballistic penetration resistance of high hard steel (HHS) by 40% with only a 23% increase in areal density. The front-facing polymer coating configuration is inexpensive and can be retrofit onto armor plates that exhibit required hardness and toughness. The coating relies on an impact-induced glass phase transition (Tg) to absorb energy, harden the coating, and reduce the strain imparted to the substrate. This effect has been exploited with other polymer coatings (e.g., butyl rubber,), which also exhibit a viscoelastic phase transition under high strain rate impact. Furthermore, laminates in the form of physically separate layers of polymer/metal stiffen the rubber material, create an impedance mismatch between the layers, and improve the mass efficiencies of armor.
In polymer-comprising armor systems, the nature of the interaction and the effect of impact depend strongly on the properties of both target and projectile. The origin of the blast and ballistic mitigation from many polymer and rubber coatings remains to be fully understood, with a variety of mechanisms likely contributing. The viscoelastic nature of polymers means that the frequency and test temperature can influence the properties of polymer-based ballistic armor, and the convolution of rate and strain effects makes quantitative analysis difficult. One important aspect of performance is the frequency of the segmental dynamics of the polymer in comparison to the strain rate during the loading. For ballistics the latter can be as high as 105 s−1 or more, and reorientation and translational modes of the polymer segments are too slow to respond on the available timescale. It would be advantageous to provide an armor system comprising a polymer where large energy absorptions could occur via solid-solid phase transitions of sufficient rapidity to mitigate impacts over the rapid timescale of a ballistic event.
These and other objects, aspects, and advantages of the present disclosure will become better understood with reference to the accompanying description and claims.